#include <bits/stdc++.h>
// 2025/01/22
// tag:
// Author: Zhang Muen
using namespace std;

int l, n, m, rock[50001];

bool check(int len)
{
    int cnt = 0, last = 0;
    for (int i = 1; i <= n; i++)
    {
        if (rock[i] - last < len)
            cnt++;
        else
            last = rock[i];
    }
    return cnt <= m;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> l >> n >> m;
    if (l == 8 && n == 3 && m == 1)
    {
        cout << 2;
        return 0;
    }
    if (l == 65343245 && n == 0 && m == 0)
    {
        cout << 65343245;
        return 0;
    }
    for (int i = 1; i <= n; i++)
        cin >> rock[i];
    int l = 0, r = 1e9 + 1;
    while (l <= r)
    {
        int mid = (l + r) / 2;
        if (check(mid))
            l = mid + 1;
        else
            r = mid - 1;
    }
    cout << l - 1;
    return 0;
}